Re: They WILL bypass the hosts file
"...this way they can bypass any controls on content that exist in the environment that might serve to block ads."
Any? I can think of a counter example, a proxy using a service that categorizes destination FQDN's that are ad services and blocks them accordingly, which I assure you does exist.
Yes, there are places that block ad services per security policy as a potential source of malware. Because, what responsibility do ad services have to ensure that the ads their many customers feed them are free from malware.
The thing I'm wondering about is how this affects ad-blocking plugins.